The full-Si molecular sieves such as S-1, S-2 and beta molecular sieve have no exchangeable cation on the framework. Their adsorption capacities for water molecule are much lower than those for organic molecules, and therefore they are highly hydrophobic. The full-Si molecular sieve can be used as membrane separation material and catalytic material, and can also be used as matrix for producing other catalytic materials. For example, the full-Si molecular sieve with a MFI-structure (known as S-1, silicalite-1) has been used as the catalyst for producing caprolactam by rearranging cyclohexanone oxime. The research about incorporating the heteroatom to the full-Si molecular sieves S-1 and beta molecular sieve, such as the synthesis of the TS-1 molecular sieve and the Sn-beta molecular sieve is highly interested.
In the currently known direct hydrothermal synthesis of the full-Si molecular sieve, the organic silicon source and/or the inorganic silicon source are generally used. The organic silicon source such as the organic silicate TEOS is costly, and the molecular sieve made therefrom has a lower content of effective component. It is difficult to increase the solid content in the crystallization product in the synthesis of the molecular sieve. In addition, in the production of the molecular sieve, a large amount of ethanol is evaporated. It is difficult to collect and reuse the evaporated ethanol. In order to reduce the cost, the inorganic silicon source is used to partly or completely substitute the organic silicon source. However, the full-Si molecular sieve made from the inorganic silicon source has a low activity. In the synthesis of the full-Si molecular sieve, the organic quaternary ammonium base or salt is generally used as the template agent. Compared with the organic quaternary ammonium base, the organic quaternary ammonium salt is cheaper; however, the full-Si molecular sieve obtained by using the organic quaternary ammonium salt as the template agent has a low activity.
Prior Art 1: CN102120589A.
Prior Art 2: CN1057976C
Prior Art 3: U.S. Pat. No. 4,061,724A
Prior Art 4: U.S. Pat. No. 4,073,865A